1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus, such as a full color copying machine, comprising a toner image retaining member for retaining a toner image temporarily.
2. Description of the Related Art
A method and apparatus for transferring two toner images on both sides of a copying paper respectively at the same time are disclosed in the Japanese patent publication (JP-B2) No. 54-28740. In the method and apparatus, a first toner image is formed on a photoconductive body at first and the toner image having been formed is transferred on a toner image retaining member primarily. After the transfer of the first toner image onto the toner image retaining member, a second toner image is formed on the photoconductive body. Furthermore, the first toner image transferred primarily from the photoconductive body onto the toner image retaining member and the second toner image formed newly on the photoconductive body are respectively transferred on both sides of a copying paper simultaneously to produce a copy of both sides. However, since an insulator belt is usually used as the toner image retaining member and the toner image formed on the photoconductive body is transferred on the insulator belt by a transfer charger arranged on the back side of the insulator belt, it is difficult to concentrate the action of the transfer charger at the transfer position where the photoconductive body and the insulator belt are in contact with each other, and therefore, portions of the photoconductive body not having passed the transfer position receive undesirable affects from the transfer charger. As the result, the toner image may be spoiled.
Also, a transferring image forming method and a transferring image forming apparatus are disclosed in the Japanese patent laid open publication (JP-A) No. 56-147166. In the method and apparatus, in order to form a plurality of toner images based on a formed electrostatic latent image, after the toner image formed on a charge retaining drum is transferred on an insulator belt primarily by pressing the charge retaining drum onto the insulator belt, the toner image transferred on the insulator belt is transferred on a copying paper secondarily. In the primary transfer process, since the transfer process of the toner image from the charge retaining member onto the insulator drum is performed by pressing both members, it is hard to perform the transfer process of the toner image stably.
Furthermore, an electrophotographic process of transferring colored electrostatic images is disclosed in the Japanese patent publication (JP-B2) No. 49-209. In the electrophotographic process, after respective colors of toner images formed on a photoconductive body are transferred on a toner image retaining drum primarily in multiple processes so as to superimpose the same thereon, the toner image superimposed on the toner image retaining drum is transferred on a copying paper secondarily. In the specification of the above publication, the transfer process for the toner image from the photoconductive body onto the toner image retaining drum is not described concretely.